Riparian forests regulate linkages between terrestrial and aquatic ecosystems, yet relationships among riparian forest development, stand structure, and stream habitats are poorly understood in many temperate deciduous forest systems. Our research has (1) described structural attributes associated with old‐growth riparian forests and (2) assessed linkages between these characteristics and in‐stream habitat structure. The 19 study sites were located along predominantly first‐ and second‐order streams in northern hardwood–conifer forests in the Adirondack Mountains of New York (USA). Sites were classified as mature forest (6 sites), mature with remnant old‐growth trees (3 sites), and old‐growth (10 sites). Forest‐structure attributes were measured over stream channels and at varying distances from each bank. In‐stream habitat features such as large woody debris (LWD), pools, and boulders were measured in each stream reach. Forest structure was examined in relation to stand age using multivariate techniques, ANOVA, and linear regression. We investigated linkages between forest structure and stream characteristics using similar methods, preceded by information‐theoretic modeling (AIC). Old‐growth riparian forest structure is more complex than that found in mature forests and exhibits significantly greater accumulations of aboveground tree biomass, both living and dead. In‐stream LWD volumes were significantly (α = 0.05) greater at old‐growth sites (200 m³/ha) compared to mature sites (34 m³/ha) and were strongly related to the basal area of adjacent forests. In‐stream large‐log densities correlated strongly with debris‐dam densities. AIC models that included large‐log density, debris‐dam density, boulder density, and bankfull width had the most support for predicting pool density. There were higher proportions of LWD‐formed pools relative to boulder‐formed pools at old‐growth sites as compared to mature sites. Old‐growth riparian forests provide in‐stream habitat features that have not been widely recognized in eastern North America, representing a potential benefit from late‐successional riparian forest management and conservation. Riparian management practices (including buffer delineation and restorative silvicultural approaches) that emphasize development and maintenance of late‐successional characteristics are recommended where the associated in‐stream effects are desired.

Forest management practices emphasizing stand structural complexity are of interest across the northern forest region of the United States because of their potential to enhance carbon storage. Our research is part of a long‐term study evaluating silvicultural treatments that promote late‐successional forest characteristics in northern hardwood‐conifer forests. We are testing the hypothesis that aboveground biomass development (carbon storage) is greater in structural complexity enhancement (SCE) treatments when compared to conventional uneven‐aged treatments. Structural complexity enhancement treatments were compared against selection systems (single‐tree and group) modified to retain elevated structure. Manipulations and controls were replicated across 2‐ha treatment units at two study areas in Vermont, United States. Data on aboveground biomass pools (live trees, standing dead, and downed wood) were collected pre‐ and post‐treatment, then again a decade later. Species group‐specific allometric equations were used to estimate live and standing dead biomass, and downed log biomass was estimated volumetrically. We used the Forest Vegetation Simulator to project “no‐treatment” baselines specific to treatment units, allowing measured carbon responses to be normalized against differences in site characteristics affecting tree growth and pre‐treatment stand structure. Results indicate that biomass development and carbon storage 10 yr post‐treatment were greatest inSCEtreatments compared to conventional treatments, with the greatest increases in coarse woody material (CWM) pools. Structural complexity enhancement treatments contained 12.67 Mg/ha carbon inCWMcompared to 6.62 Mg/ha in conventional treatments and 8.84 Mg/ha in areas with no treatment. Percentage differences between post‐treatment carbon and simulated/projected baseline values indicate that carbon pool values inSCEtreatments returned closest to pre‐harvest or untreated levels over conventional treatments. Total carbon storage inSCEaboveground pools was 15.90% less than that projected for no‐treatment compared to 44.94% less in conventionally treated areas. Results from classification and regression tree models indicated treatment as the strongest predictor of aboveground C storage followed by site‐specific variables, suggesting a strong influence of both on carbon pools. Structural enhancement treatments have the potential to increase carbon storage in managed northern hardwoods. They offer an alternative for sustainable management integrating carbon, associated climate change mitigation benefits, and late‐successional forest structure and habitat.

Temperate old‐growth forests are known to have ecological characteristics distinct from younger forests, but these have been poorly described for the remaining old‐growth Picea abies–Abies alba forests in the eastern Carpathian mountains. In addition, recent studies suggest that old‐growth forests may be more significant carbon sinks than previously recognized. This has stimulated interest in quantifying aboveground carbon stocks in primary forest systems. We investigated the structural attributes and aboveground biomass in two remnant old‐growth spruce–fir stands and compared these against a primary (never logged) mature reference stand. Our sites were located in the Gorgany Nature Reserve in western Ukraine. Overstory data were collected using variable radius plots; coarse woody debris was sampled along line intercept transects. Differences among sites were assessed using non‐parametric statistical analyses. Goodness‐of‐fit tests were used to evaluate the form of diameter distributions. The results strongly supported the hypothesis that old‐growth temperate spruce–fir forests have greater structural complexity compared to mature forests, including higher densities of large trees, more complex horizontal structure, and elevated aboveground biomass. The late‐successional sites we sampled exhibited rotated sigmoid diameter distributions; these may reflect natural disturbance dynamics. Old‐growth Carpathian spruce–fir forests store on average approximately 155–165 Mg ha⁻¹ of carbon in aboveground tree parts alone. This is approximately 50% higher than mature stands. Given the scarcity of primary spruce–fir forests in the Carpathian region, remaining stands have high conservation value, both as habitat for late‐successional species and as carbon storage reservoirs.

Riparian forest restoration can be severely constrained by tree seedling mortality. I evaluated the effects of tree shelters and planting density on herbivory and seedling mortality at a restoration site in the Lake Champlain Basin of Vermont. Eighteen experimental units were established along a 5th-order stream and planted with bare-root seedlings of seven species associated with northern hardwood floodplain forests. Two treatments were applied in a factorial design: shelters versus no shelters and high versus low planting density. Mortality and herbivory data were collected over three growing seasons. Survivorship declined to 56.4% after three growing seasons and varied significantly by species. Planting density, presence/absence of shelters, and their interaction had significant effects on survival, browse, or girdling intensity when tested for all species combined. Browse rates were high (44%), whereas girdling rates were low (3.4%). Both browse (P < 0.001) and girdling (P = 0.022) contributed to seedling mortality. High rates of deer browse on seedlings in shelters were due, in part, to the short height (60 cm) of the shelters, suggesting a need for taller shelters. A large portion (39%) of dead seedlings were neither browsed nor girdled, signaling the importance of other mortality agents. An adaptive approach is recommended to compensate for high seedling mortality and the limited effectiveness of protective devices.

Demand for forest bioenergy fuel is increasing in the northern forest region of eastern North America and beyond, but ecological impacts, particularly on habitat, of bioenergy harvesting remain poorly explored in the peer‐reviewed literature. Here, we evaluated the impacts of bioenergy harvests on stand structure, including several characteristics considered important for biodiversity and habitat functions. We collected stand structure data from 35 recent harvests in northern hardwood–conifer forests, pairing harvested areas with unharvested reference areas. Biometrics generated from field data were analyzed using a multi‐tiered nonparametric uni‐ and multivariate statistical approach. In analyses comparing harvested to reference areas, sites that had been whole‐tree harvested demonstrated significant differences (relative negative contrasts, P < 0.05) in snag density, large live‐tree density, well‐decayed downed coarse woody debris volume, and structural diversity index (H) values, while sites that had not been whole‐tree harvested did not exhibit significant differences. Classification and regression tree (CART) analyses suggested that the strongest predictors of structural retention, as indicated by downed woody debris volumes and H index, were silvicultural treatment and equipment type rather than the percentage of harvested volume allocated to bioenergy uses. In general, bioenergy harvesting impacts were highly variable across the study sites, suggesting a need for harvesting guidelines aimed at encouraging retention of ecologically important structural attributes.